1. Field of the Invention
The invention is related to the field of optical measurement instruments, and in particular, to a spatial frequency optical measurement instrument and method.
2. Statement of the Problem
A turbidimeter or nephelometer is an instrument used for the determination of the concentration and/or size of particles in a suspension media. A nephelometer generally refers to an optical instrument for detecting and/or measuring suspended particulates in a liquid or gas colloid. In contrast, a turbidimeter generally refers to an optical instrument for detecting and/or measuring particulate matter in water. Consequently, the suspension media can comprise water.
In the prior art, light is projected through a sample material. The sample material comprises a suspension media and an unknown concentration of particles. The particles within the suspension scatter the impinging light by a complex interaction of reflection, diffraction, and refraction. A portion of the incident light is scattered from the particles and is received by a detector. The detector is commonly a silicon diode or other photosensitive device, typically positioned approximately 90 degrees to the incident light source.
In order to quantify the amount of particles within the suspension media, a comparison must be made of the received scattered light to a scattered light level obtained using a similar suspension media of known particulate concentration. Subsequently, unknown particulate concentrations can be compared to known calibration values and can be determined by estimation or extrapolation from the calibration values.
FIG. 1 shows a prior art turbidimeter/nephelometer. A light source 1 emits light into a sample material 4 contained within a sample chamber 3. Optical components may collimate and/or focus the light toward the sample chamber 3. Light from the light source 1 can either propagate through the sample material 4 unimpeded or can interact with the sample material 4 by impinging on particles in the material. Light impinging on a particle can scatter in multiple directions, including a backward direction, a forward direction, and can scatter sideways, such as along a path substantially at ninety degrees to the incident beam. Light scattered to the side may impinge on a detector 2a. Unscattered light may be received by a second detector 2b that can be used to determine an intensity of the light from the light source 1. The detector 2a converts photon energy into an electrical signal by means of a photoelectric effect. The electrical signal, usually weak or low in signal strength, can be amplified and can subsequently be processed in a processing system in order to determine a turbidity of the sample material 4. The determined turbidity can be output to a meter or other useful indicator.
Optical measurement instruments used to measure scattering effects rely almost exclusively on a method of measurement that assesses changes in intensity of light or radiant energy. The light or radiant energy can be either transmitted through or reflected from the sample. The measurement of scattering can be used for a determination of the particulate concentration of the scattering constituent or can be used for a determination of a surface condition/finish of the sample.
Prior art methods for determination of turbidity by nephelometric means rely on an amplitude detection of the scattered signal from a turbid sample. The prior art measures only the intensity of the received light.
The prior art has drawbacks. In the prior art, the signal values corresponding to the received light intensity are very small for low concentrations of particles and are ideally zero when no particles are present in the suspension media. Consequently, the limit of detection is a function of a signal-to-noise ratio (SNR) of the detector, the intensity of the light source, and the amount of stray light impinging on the detector, wherein the stray light is not associated with the particles in the suspension media. In addition, the accuracy of a prior art nephelometric assay is further degraded by drift or changes in the intensity of the light source or sensitivity of the detector due to temperature changes or wear. In the prior art, the accuracy is further degraded by any light absorption by the suspension media, since prior art methods rely on absolute intensity measurements or on a ratio of the intensity of the received scattered light to the intensity of the emitted light. Changes in the light intensity impinging upon the detector, not associated with the measure of turbidity, produces an error in the measured response. Consequently, any changes in color or absorption of the suspension media can also result in false determination of the concentration of particles in a suspension, since this also results in a change in the absolute measure of the intensity of the light.
Prior art methods have been devised to reduce or counter these effects, such as dual beam, dual wavelength, or ratio methods, but limitations arise due to the increased cost and complexity of adding secondary or alternate light sources and detectors such as non-uniform degradation of surfaces due to bubbles, biological films, or dirt.
There remains a need for a nephelometric particle assay that does not depend on the explicit quanta/intensity of received light.
Aspects
One aspect of the invention includes a spatial frequency optical measurement instrument, comprising:
a spatial frequency mask positioned in a light path and configured to encode light with spatial frequency information;
a light receiver positioned to receive the light encoded with the spatial frequency information, wherein the light encoded with the spatial frequency information has been interacted with a sample material; and
a processing system coupled to the light receiver and configured to determine a change in the spatial frequency information due to the interaction of the light with the sample material.
Preferably, the instrument, with interacting the light with the sample material comprising substantially passing the light through the sample material.
Preferably, the instrument, with interacting the light with the sample material comprising substantially reflecting the encoded light off of the sample material.
Preferably, one or more optical components configured to define a spatial frequency image of the spatial frequency mask at the light receiver, with the spatial frequency image substantially including the spatial frequency information.
Preferably, a light source configured to emit the light along the light path.
Preferably, the light source further comprises a powered light source.
Preferably, the light source further comprises an ambient light source.
Preferably, the spatial frequency mask being located before the sample material and encoding light that has not interacted with the sample material.
Preferably, the spatial frequency mask being located after the sample material and encoding light that has interacted with the sample material.
Preferably, the spatial frequency mask comprises light blocking and light transmitting regions that encode the spatial frequency information.
Preferably, the spatial frequency mask comprises a series of spatially varying blocking and light transmitting regions that encode the spatial frequency information.
Preferably, the spatial frequency mask comprises a series of apertures that encode the spatial frequency information.
Preferably, the spatial frequency mask comprises a series of spatially varying apertures that encode the spatial frequency information.
Preferably, a light path length through the sample material can be varied in order to vary the change in spatial frequency information.
Preferably, the light path includes one or more excursions through or reflections from the sample material.
Preferably, the light path includes one or more excursions through or reflections from the sample material and wherein the number of excursions or reflections can be varied in order to vary the spatial frequency information.
Preferably, the spatial frequency information being substantially independent of the intensity or composition of the light.
Preferably, the change in the spatial frequency information includes a change to a content or organization of the spatial frequency information.
Preferably, the change in the spatial frequency information includes a change to one or more of a line, an edge, a bar pattern, a sinusoidal pattern, or a point function of the spatial frequency information.
Preferably, determining the change in the spatial frequency information comprises determining a change in the spatial frequency information from a predetermined standard.
Preferably, determining the change in the spatial frequency information comprises determining a change in contrast in the spatial frequency information from a predetermined contrast standard.
Preferably, the processing system further determines a particulate concentration in a media of the sample material based on the change in the spatial frequency information.
Preferably, determining the particulate concentration further comprises comparing the spatial frequency information to one or more predetermined particulate concentration images and interpolating and/or extrapolating a particulate concentration value from the one or more predetermined particulate concentration images.
Preferably, the processing system further determines one or more surface characteristics of the sample material.
Preferably, determining the one or more surface characteristics further comprises comparing the spatial frequency information to one or more predetermined surface images and interpolating and/or extrapolating the one or more surface characteristics from the one or more predetermined surface images.
Preferably, a first portion of the encoded light is reflected onto a first light receiver without interacting with the sample material and wherein a second portion of the encoded light is interacted with the sample material and wherein the second portion of the encoded light is compared to the first portion.
Preferably, the light comprising a first light portion interacting with the spatial frequency mask and the sample material to form a spatial frequency image and with the light further comprising a second light portion interacting with a predetermined standard material to form a predetermined standard image, wherein the change in the spatial frequency information comprising a difference between the spatial frequency image and the predetermined standard image.
Another aspect of the invention comprises a spatial frequency optical measurement method, comprising:
encoding light with spatial frequency information;
interacting the light with a sample material; and
determining a change in the spatial frequency information due to the interaction of the light with the sample material.
Preferably, the method further comprises interacting the light with a spatial frequency mask positioned in a light path.
Preferably, the method further comprises interacting the light with a spatial frequency mask positioned in a light path, with the spatial frequency mask comprising light blocking and light transmitting regions that encode the spatial frequency information.
Preferably, the method further comprises interacting the light with a spatial frequency mask positioned in a light path, with the spatial frequency mask comprising a series of spatially varying light blocking and light transmitting regions that encode the spatial frequency information.
Preferably, the method further comprises interacting the light with a spatial frequency mask positioned in a light path, with the spatial frequency mask comprising a series of apertures that encode the spatial frequency information.
Preferably, the method further comprises interacting the light with a spatial frequency mask positioned in a light path, with the spatial frequency mask comprising a series of spatially varying apertures that encode the spatial frequency information.
Preferably, the method further comprises interacting the light with the sample material comprising substantially passing the light through the sample material.
Preferably, the method further comprises interacting the light with the sample material comprising substantially reflecting the encoded light off of the sample material.
Preferably, the method further comprises a light path length through the sample material can be varied in order to vary the change in spatial frequency information.
Preferably, the method further comprises a light path includes one or more excursions through or reflections from the sample material.
Preferably, the method further comprises a light path includes one or more excursions through or reflections from the sample material and wherein a number of excursions or reflections can be varied in order to vary the change in spatial frequency information.
Preferably, the method further comprises spatial frequency information being substantially independent of the intensity or composition of the light.
Preferably, the method further comprises the change in the spatial frequency information including a change to a content or organization of the spatial frequency information.
Preferably, the method further comprises the change in the spatial frequency information including a change to one or more of a line, an edge, a bar pattern, a sinusoidal pattern, or a point function of the spatial frequency information.
Preferably, the method further comprises determining the change in the spatial frequency information comprising determining a change in the spatial frequency information from a predetermined standard.
Preferably, the method further comprises determining the change in the spatial frequency information comprising determining a change in contrast in the spatial frequency information from a predetermined contrast standard.
Preferably, the method further comprises the processing system further determining a particulate concentration in a media of the sample material based on the change in the spatial frequency information.
Preferably, the method further comprises determining the particulate concentration further comprising:
comparing the spatial frequency information to one or more predetermined particulate concentration images; and
interpolating and/or extrapolating a particulate concentration value from the one or more predetermined particulate concentration images.
Preferably, the method further comprises the processing system further determining one or more surface characteristics of the sample material based on the change in the spatial frequency information.
Preferably, the method further comprises determining the one or more surface characteristics further comprising:
comparing the spatial frequency information to one or more predetermined surface images; and
interpolating and/or extrapolating the one or more surface characteristics from the one or more predetermined surface images.
Preferably, the method further comprises a first portion of the encoded light is reflected onto a first light receiver without interacting with the sample material and wherein a second portion of the encoded light is interacted with the sample material and wherein the second portion of the encoded light is compared to the first portion.
Preferably, the method further comprises the light comprising a first light portion interacting with the spatial frequency mask and the sample material to form a spatial frequency image and with the light further comprising a second light portion interacting with a predetermined standard material to form a predetermined standard image, wherein the change in the spatial frequency information comprising a difference between the spatial frequency image and the predetermined standard image.
Another aspect of the invention comprises a spatial frequency optical measurement method, comprising:
interacting light with a sample material;
reflecting and encoding the light with spatial frequency information; and
determining a change in the spatial frequency information due to the interaction of the light with the sample material.
Preferably, the method further comprises reflecting and encoding the light comprising interacting the light with a reflective spatial frequency mask positioned in a light path.
Preferably, the method further comprises reflecting and encoding the light comprising interacting the light with a reflective spatial frequency mask positioned in a light path, with the reflective spatial frequency mask comprising light reflecting and non-reflecting regions that encode the spatial frequency information.
Preferably, the method further comprises reflecting and encoding the light comprising interacting the light with a reflective spatial frequency mask positioned in a light path, with the reflective spatial frequency mask comprising a series of spatially varying light reflecting and non-reflecting regions that encode the spatial frequency information.
Preferably, the method further comprises reflecting and encoding the light comprising interacting the light with a reflective spatial frequency mask positioned in a light path, with the reflective spatial frequency mask comprising a series of apertures that encode the spatial frequency information.
Preferably, the method further comprises reflecting and encoding the light comprising interacting the light with a reflective spatial frequency mask positioned in a light path, with the reflective spatial frequency mask comprising a series of spatially varying apertures that encode the spatial frequency information.
Preferably, the method further comprises interacting the light with the sample material comprising substantially passing the light through the sample material.
Preferably, the method further comprises a light path length through the sample material can be varied in order to vary the change in spatial frequency information.
Preferably, the method further comprises a light path includes one or more excursions through the sample material.
Preferably, the method further comprises a light path includes one or more excursions through the sample material and wherein a number of excursions can be varied in order to vary the spatial frequency information.
Preferably, the method further comprises spatial frequency information being substantially independent of the intensity or composition of the light.
Preferably, the method further comprises the change in the spatial frequency information including a change to a content or organization of the spatial frequency information.
Preferably, the method further comprises the change in the spatial frequency information including a change to one or more of a line, an edge, a bar pattern, a sinusoidal pattern, or a point function of the spatial frequency information.
Preferably, the method further comprises determining the change in the spatial frequency information comprising determining a change in the spatial frequency information from a predetermined standard.
Preferably, the method further comprises the change in the spatial frequency information comprising determining a change in contrast in the spatial frequency information from a predetermined contrast standard.
Preferably, the method further comprises the processing system further determining a particulate concentration in a media of the sample material based on the change in the spatial frequency information.
Preferably, the method further comprises the particulate concentration further comprising:
comparing the spatial frequency information to one or more predetermined particulate concentration images; and
interpolating and/or extrapolating a particulate concentration value from the one or more predetermined particulate concentration images.
Preferably, the method further comprises the processing system further determining one or more surface characteristics of the sample material based on the change in the spatial frequency information.
Preferably, the method further comprises the one or more surface characteristics further comprising:
comparing the spatial frequency information to one or more predetermined surface images; and
interpolating and/or extrapolating the one or more surface characteristics from the one or more predetermined surface images.
Preferably, the method further comprises the light comprising a first light portion interacting with the spatial frequency mask and the sample material to form a spatial frequency image and with the light further comprising a second light portion interacting with a predetermined standard material to form a predetermined standard image, wherein the change in the spatial frequency information comprising a difference between the spatial frequency image and the predetermined standard image.